Ecological Consequences of Altered Floodplain Hydrology for Catahoula Lake

Richard F Keim, School of Renewable Natural Resources, Louisiana State University, Baton Rouge, LA, 70803, Lincoln Dugué, School of Renewable Natural Resources, Louisiana State University, Baton Rouge, LA, 70803, Karen Latuso, School of Renewable Natural Resources, Louisiana State University, Baton Rouge, LA, 70803; and Sanjeev JoshiSchool of Renewable Natural Resources, Louisiana State University, Baton Rouge, LA, 70803 add emails

The hydrology of Catahoula Lake, a large, backswamp lake with large annual fluctuations in its water level near the confluence of these rivers, is driven by local rainfall but also by backwater from the Mississippi, Red, and Atchafalaya rivers. Geomorphic modification for navigation and flood control has changed hydrologic conditions at Catahoula Lake. Gauge analyses show that backwater influence has decreased from 207 to 120 days per year between 1880 and 2010. Recent sedimentation is ~0.3 cm/yr, which is increased ~225% from the pre-settlement rate, and there has been a shift from mixed coastal-plain and Mississippi Alluvial Valley sediments to dominance by acidic, coastal-plain sediments in the past ~60 yr, coinciding with decreased connectivity to the Mississippi River. Our best estimate is the lakebed is ~20 cm higher, that current lake levels are lower in the high-water spring, less variable in the fall dry period, and lack the extreme high water events compared to 100+ years ago. Palynological results indicate the lake bed has likely been free of woody vegetation for several thousand years. However, woody vegetation has been encroaching into the lake bed and aerial imagery and tree rings show the rate of encroachment has increased 249% since major hydrologic alterations in the 1960s. Maintaining non-woody cover through management is essential to sustain ecologic function of the lake as important waterbird habitat, but the causes of ecological change appear to be multiple and difficult to manipulate in the context of regional water management.

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